This invention relates generally to the storage and display of waveforms by a digital oscilloscope, and in particular to a digital system for detecting and storing waveforms which differ from a stored reference waveform.
Conventional digital oscilloscopes record and display time-varying electrical phenomena by converting analog signals to digital representations which are then stored as a complete waveform to be subsequently regenerated for display on a cathode-ray tube screen. Typically, digital oscilloscopes operate in independent acquisition (or store) and display modes, having separate waveform memories for each mode, permitting the use of independent and perhaps different clocking rates. Because of the limited memory space available for waveform storage and the amount of elapsed time between waveform acquisition and subsequent display, various operating modes have been developed for user convenience.
One such operating mode is the multiple waveform storage system described in U.S. Pat. No. 4,198,683 to Thomas P. Dagostino and assigned to the assignee of the present invention. Here, several waveforms are acquired in seriatum and stored in separate respective waveform memories and then displayed in chronological sequence by a history controller and memory counter. When a new waveform is acquired, the oldest waveform is discarded.
Another operating mode is the waveform storage system described in U.S. Pat. No. 4,271,486 to Thomas P. Dagostoino and Luis J. Navarro and assigned to the assignee of the present invention. In this mode, maximum signal deviations along a waveform are detected and stored at predetermined intervals so that a composite envelope of the signal may be displayed.
Often it is desired to monitor repetitive electrical signals for occasional changes or random occurrences, such as glitches, missing pulses, and so forth, and to store such changed phenomena for display, perhaps in comparison with a reference waveform. However, such monitoring can be very tedious to a user.